US20130339767A1 - Variable power over ethernet based on link delay measurement - Google Patents
Variable power over ethernet based on link delay measurement Download PDFInfo
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- US20130339767A1 US20130339767A1 US13/968,385 US201313968385A US2013339767A1 US 20130339767 A1 US20130339767 A1 US 20130339767A1 US 201313968385 A US201313968385 A US 201313968385A US 2013339767 A1 US2013339767 A1 US 2013339767A1
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F1/00—Details not covered by groups G06F3/00 - G06F13/00 and G06F21/00
- G06F1/26—Power supply means, e.g. regulation thereof
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L12/00—Data switching networks
- H04L12/02—Details
- H04L12/10—Current supply arrangements
Definitions
- Ethernet communications provide high speed data communications over a communications link between communication nodes (or network devices) that are operating according to the IEEE 802.3 Ethernet standard.
- the communications medium between the two nodes can be twisted pair wires for Ethernet, or other types of communications medium that are appropriate.
- Powers over Ethernet (POE) communication systems may provide power and data communications over a common communications link.
- a power source device e.g., power source equipment (PSE)
- PSE power source equipment
- PD powered device
- the DC power is transmitted simultaneously from PSE to PD over the same communications medium that high speed data is transmitted between PD and PSE. In this manner, a separate power cable may be avoided or unnecessary for the PD.
- PSE power source equipment
- the PSE device may be a data switch, a computer, or other device, for example.
- APSE may include one or more data ports (or Ethernet ports). Each port may include a transceiver to transmit and receive data over a data link or communications medium (e.g., one or more twisted pair wires, or Ethernet cable) that may be connected to a data port on another device or node.
- data ports and their corresponding links can be interchangeably referred to as data channels, communication links, data links, etc, for ease of discussion.
- Typical PD devices that use POE to receive power may include a wide variety of devices, such as, for example, Internet Protocol (IP) phones (Voice over IP (VoIP) phones), wireless access points, personal computing devices, such as a personal computer or a laptop computer, handheld devices, a camera (e.g., IP security camera), a print server, or other electronic device.
- IP Internet Protocol
- VoIP Voice over IP
- personal computing devices such as a personal computer or a laptop computer, handheld devices, a camera (e.g., IP security camera), a print server, or other electronic device.
- IP Internet Protocol
- VoIP Voice over IP
- personal computing devices such as a personal computer or a laptop computer, handheld devices, a camera (e.g., IP security camera), a print server, or other electronic device.
- IP Internet Protocol
- VoIP Voice over IP
- personal computing devices such as a personal computer or a laptop computer, handheld devices, a camera (e.g., IP security camera), a print server, or other electronic device.
- a PSE device may typically have a POE power budget, which may indicate a maximum amount of power (e.g., 200 W) available to provide to one or more connected PDs (connected via one or more Ethernet ports).
- IEEE 802.3af allows a maximum length of 100 meters for an Ethernet cable or link between aPSE and PD.
- PSE devices In allocating power to a PD, PSE devices typically assume that each PD is connected via a maximum length (1OOm) cable. Although, in some cases, PDs may be connected to the PSE via shorter length links or cables.
- Various embodiments are disclosed relating to variable power over Ethernet based on a link delay measurement.
- FIG. 1 is a high level illustration of a Power over Ethernet (POE) system 100 that provides both DC power and data communications over a common data communications medium according to an example embodiment.
- POE Power over Ethernet
- FIG. 2 provides a more detailed circuit diagram of the POE system 100 , where PSE 102 provides DC power to PD 106 over conductor pairs 104 and 110 , for example.
- FIG. 3 is a timing diagram illustrating a technique that may be used to determine a propagation delay of a communications link based on a message exchange between two nodes according to an example embodiment.
- FIG. 4 is a flow chart illustrating operation of a power source equipment according to an example embodiment.
- FIG. 5 is a flow chart illustrating operation of a PSE according to another example embodiment.
- FIG. 6 is a flow chart illustrating operation of a PD according to an example embodiment.
- FIG. 1 is a high level illustration of a Power over Ethernet (POE) system 100 that provides both DC power and data communications over a common data communications medium according to an example embodiment.
- PSE power source equipment
- PD powered device
- the PSE 102 and PD 106 also include data transceivers (transmitter/receiver) that transmit and receive data according to, e.g., IEEE 802.3 Ethernet standard.
- POE may refer to providing power over a communications link either for Ethernet or other networking standard.
- a more general term may be, for example, power over networking, which may include providing power over any networking or communications link (including POE).
- the PSE 102 includes a physical layer device on the PSE side that transmits and receives high speed data with a corresponding physical layer device in the PD 106 . Accordingly, the power transfer between the PSE 102 and the PD 106 may occur simultaneously with the exchange of high speed data over the conductors 104 , 110 .
- the PSE 102 may be a data switch having multiple ports that is in communication with one or more PD devices, such as Internet phones, or wireless access points, or other network devices.
- the conductor pairs 104 and 110 may carry high speed differential data communications.
- the conductor pairs 104 and 110 each include one or more twisted wire pairs, or any other type of cable or communications media capable of carrying the data transmissions and DC power transmissions between the PSE and PD.
- the conductor pairs 104 and 110 can include multiple twisted pairs, for example four twisted pairs for 10 Gigabit Ethernet. In 10/100 Ethernet, only two of the four pairs carry data communications, and the other two pairs of conductors are unused.
- conductor pairs 104 , 110 may also be referred to as wires, Ethernet cables, communication (or data) links, lines, communication medium or communication media, for ease of discussion.
- FIG. 2 provides a more detailed circuit diagram of the POE system 100 , where PSE 102 provides DC power to PD 106 over conductor pairs 104 and 110 , for example.
- PSE 102 includes a transceiver physical layer device (or PHY) 202 having full duplex transmit and receive capability through differential transmit port 204 and differential receive port 206 .
- transceivers may be referred to as PHYs.
- a first transformer 208 couples high speed data between the transmit port 204 and the first conductor pair 104 .
- a second transformer 212 couples high speed data between the receive port 206 and the second conductor pair 110 .
- the respective transformers 208 and 212 pass the high speed data to and from the transceiver 202 , but isolate any low frequency or DC voltage from the transceiver ports, which may be sensitive to large voltage values.
- the first transformer 208 includes primary and secondary windings, where the secondary winding (on the conductor side) includes a center tap 210 .
- the second transformer 212 includes primary and secondary windings, where the secondary winding (on the conductor side) includes a center tap 214 .
- the DC voltage supply 216 generates an output voltage that is applied across the respective center taps of the transformers 208 and 212 on the conductor side of the transformers.
- the center tap 210 is connected to a first output of a DC voltage supply 216
- the center tap 214 is connected to a second output of the DC voltage supply 216 .
- the transformers 208 and 212 isolate the DC voltage from the DC supply 216 from the sensitive data ports 204 , 206 of the transceiver 202 .
- An example DC output voltage is 48 volts, but other voltages could be used depending on the voltage/power requirements of the PD 106 .
- the PSE 102 further includes a PSE controller 218 that controls the DC voltage supply 216 , e.g., based on a classification load provided by the PD (based on the POE classification of the PD) and/or based on a determined length (or link delay or propagation delay) of a communications link (e.g. Ethernet cable) connecting the PD 106 and PSE 102 .
- a communications link e.g. Ethernet cable
- the length of the cable or communications link connecting the PSE 102 and PD 106 may be determined based on a propagation time for a packet transmitted across the communications link that connects the PD 106 and PSE 102 .
- PSE 102 determines that the communications link (including conductor pairs 104 , 110 ) between PD 106 and PSE 102 is shorter than the maximum length of 1OOm, then the PSE may provide less, or may decrease, power to the PD.
- the PSE controller 218 may detect and validate a compatible PD, determine a power classification signature for the validated PD, determine a length of a communications link or cable between the PSD and PD, determine an amount of power to be supplied to the PD, and provide or supply power to the PD, monitors the power, and reduces or removes the power from the PD when the power is no longer requested or required.
- the PSE finds the PD to be non-compatible, the PSE can prevent the application of power to that PD device, protecting the PD from possible damage.
- the PD 106 includes a transceiver physical layer device 219 having full duplex transmit and receive capability through differential transmit port 236 and differential receive port 234 .
- a third transformer 220 couples high speed data between the first conductor pair 104 and the receive port 234 .
- a fourth transformer 224 couples high speed data between the transmit port 236 and the second conductor pair 110 .
- the respective transformers 220 and 224 pass the high speed data to and from the transceiver 219 , but isolate any low frequency or DC voltage from the sensitive transceiver data ports.
- the third transformer 220 includes primary and secondary windings, where the secondary winding (on the conductor side) includes a center tap 222 .
- the fourth transformer 224 includes primary and secondary windings, where the secondary winding (on the conductor side) includes a center tap 226 .
- the center taps 222 and 226 supply the DC power carried over conductors 104 and 110 to the representative load 108 of the PD 106 , where the load 108 represents the dynamic power draw needed to operate PD 106 .
- a DC-DC converter 230 may be optionally inserted before the load 108 to step down the voltage as necessary to meet the voltage requirements of the PD 106 . Further, multiple DC-DC converters 230 may be arrayed in parallel to output multiple different voltages (3 volts, 5 volts, 12 volts, for example) to supply different loads 108 of the PD 106 .
- the PD 106 further includes a PD controller 228 that monitors the voltage and current on the PD side of the POE configuration.
- the PD controller 228 further provides the necessary impedance signatures (e.g., a resistance of approximately 25 kilo-ohms) on the return conductor 110 during initialization, so that the PSE controller 218 will recognize the PD as a valid POE device, and be able to classify its power requirements.
- a direct current (I DC ) 238 flows from the DC power supply 216 through the first center tap 210 , and divides into a first current (I 1 ) 240 and a second current (I 2 ) 242 that is carried over conductor pair 104 .
- the first current (I 1 ) 240 and the second current (I 2 ) 242 then recombine at the third center tap 222 to reform the direct current (I DC ) 238 so as to power PD 106 .
- the direct current NO 238 flows from PD 106 through the fourth center tap 226 , and divides for transport over conductor pair 110 .
- the return DC current recombines at the second center tap 214 , and returns to the DC power supply 216 .
- a first communication signal 244 and/or a second communication signal 246 are simultaneously differentially carried via the conductor pairs 104 and 110 between the PSE 102 and the PD 106 . It is important to note that the communication signals 244 and 246 are differential signals that typically are not affected by the DC power transfer.
- detection and power classification of a PD may be a part of the process of supplying power to a PD using POE.
- the PD controller 228 further provides the necessary impedance signatures (e.g., a resistance of approximately 25 kilo-ohms) on the return conductor 110 during initialization, so that the PSE controller 218 will recognize the PD as a valid POE device.
- the PSE 102 may determine an amount of power to be provided to PD 106 via POE based at least in part on a determined link delay or length of the communications link ( 104 , 110 ) connecting PD 106 and PSE 102 .
- Either PSE 102 and/or PD 106 may determine a length of a communications link or a propagation delay of the communications link (conductors 104 , 110 ) that connects PD 106 and PSE 102 .
- the amount power to be provided to PD 106 may be determined (e.g, at least in part) based on both a power classification and a length of the communications link (or link delay).
- a classification load or signature supplied by PD 106 may be varied or adjusted based on the determined length of the communications link or the propagation delay of the communications link that connects PD 106 and PSE 102 , or other power adjustment or selection may be performed based on a determined link delay or length of the communications link, as described in greater detail below.
- POE Power classification will be described, followed by a description of measuring or determining a communications link delay (or propagation delay) or measuring the length of the communications link (conductors 104 , 110 ), and then adjusting or determining the POE power supplied to the PD 106 based, at least in part, on the length of the communications link or propagation delay of the communications link.
- PD controller 228 of PD 106 may provide a classification signature (or classification load or classification resistance) onto the line, e.g., onto conductor 110 to indicate power requirements of the PD 106 , for example.
- the PSE 102 may apply a voltage, e.g., across the conductors or communication links 104 , 110 of between 14.5 volts and 20.5 volts, and detects the resulting classification current.
- the resulting classification current may be determined based on V/R class , where V is the voltage applied to the conductors by PSE 102 and R class is the classification load (resistance) or classification signature applied by PD 106 during the power classification.
- the power range provided by a PSE depends on the resulting classification current detected by the PSE, e.g., according to Table 1 below.
- Table 1 merely illustrates some example power and current values for different PD classifications, and the disclosure is not limited thereto.
- a PSE 102 may determine or measure a length of a communications link (e.g., length of an Ethernet cable or length of conductors 104 , 110 ) connected between the PSE 102 and a connected PD 106 . The PSE 102 may then adjust (e.g., decrease) an amount of power provided via POE to the PD 106 based on the length of the communications link.
- a communications link e.g., length of an Ethernet cable or length of conductors 104 , 110
- PSE controller 218 of PSE 102 may determine a length of a communications link (e.g., conductors 104 , 110 ) based on a propagation delay across the link (or link delay). Once the propagation delay across the link is known, the length of the link may be determined. For example, the length of a communications link (e.g., lengths of the Ethernet cable or conductors 104 , 110 connecting PD 106 and PSE 102 ) may be determined based on Eqn. (1), for example.
- Length(of communications link) (prop. delay)(2 ⁇ 3 C) Eqn. (1)
- prop. delay is the measured or determined propagation delay for the link (in seconds)
- C is the speed of light (approximately 3 ⁇ 10 8 meters/second).
- the propagation speed on the link has been determined to be 2 ⁇ 3 of the speed of light, or 2 ⁇ 3C.
- the PSE 102 may then determine or adjust (or vary) the power supplied to the PD 106 via POE based on the length of the communications link connecting PSE 102 and PD 106 (or based on the link delay). There are several different ways in which PSE 102 may adjust or decrease the amount of power supplied to the PD.
- a portion of this allocated power may be required by the PD 106 (e.g., 1.84 W), and the remainder (2 W) may be required to provide such power via the 100 meter communications link, since power will be consumed or dissipated (via the link) to provide power to the PD 106 via the link due to the resistance of the communications link.
- the total resistance of the communications link may typically increase as the length of the link increases.
- a 1 OOM link may have approximately twice as much resistance as a 50M link, assuming the links are otherwise the same or very similar.
- 3.84 W maximum power may be specified, including 1.84 W to be provided to the PD 106 , plus a total link power of 2 W may be used for the link (in this example), assuming a maximum length 1OOm link.
- the PSE 102 may decrease the supplied (or allocated) power by 1 W (to 2.84 W).
- the lengths of the cable is only 10 meters, then only 1/10 th of the power allocated to the cable (0.2 W in this example) may be necessary to supply the 1.84 W to PD 106 .
- the supplied power may be decreased from 3.84 W to 2.04 W due to use of a shorter communications link or Ethernet cable to connect PD 106 and PSE 102 .
- a propagation delay and/or determined length for a communications link may be used to adjust or decrease supplied POE (or power over network) power. This is merely one example technique and others may be used as well to determine a power savings due to a shorter or actual length of the link or Ethernet cable.
- a lower and more accurate amount of power may (at least in some cases) be allocated by PSE 102 to PD 106 from the PSE's power budget.
- measuring or estimating the length of the communications link based on the propagation delay may allow a more accurate determination of the actual power required for the connected PD 106 .
- This may allow unused power in the PSE's power budget to be used to power additional PDs, or may allow a PSE to power a same number of PDs using a lower amount of power or using a smaller power supply, for example.
- PD 106 may measure or determine a length of the communications link (e.g., length of conductors 104 , 110 ) or Ethernet cable that connects PD 106 and PSE 102 based on the propagation delay for the communications link. PD 106 may determine or estimate a length of the communications link that connects PD 106 and PSE 102 , e.g., based on Eqn. (1), or using other technique.
- a length of the communications link e.g., length of conductors 104 , 110
- Ethernet cable that connects PD 106 and PSE 102 based on the propagation delay for the communications link.
- PD 106 may determine or estimate a length of the communications link that connects PD 106 and PSE 102 , e.g., based on Eqn. (1), or using other technique.
- PD 106 may send a packet to PSE 102 indicating the actual length of the communications link or the propagation delay of the communications link (or associated reduction in power if a cable shorter than 100 m is used), or indicating an actual power to be supplied to PD 106 .
- PSE 102 may then adjust the power supplied to PD 106 based on the actual length of the link (or based on link propagation delay) if PD 106 has indicated the length of the communications link (or propagation delay for the link), or PSE 102 may supply the requested power to PD 106 if PD 106 has indicated a requested power (taking into account length of the communications link).
- PD 106 may provide a classification resistance or classification signature to PSE 102 based, at least in part, on the actual or measured length of the communications link or based on the measured or determined propagation delay for the communications link that connects PD 106 and PSE 102 .
- PD 106 may require a base power of 6 W (for the PD itself), plus 2 W associated with a maximum link length of 100 meters, requiring a total power of 8 W to be supplied by the PSE 102 . If a communications link of length equal to 10 meters is used to connect PD 106 and PSE 102 (instead of 100 meters), a power savings of 1.8 W may result (for example), since only 10% of 2 W (or 0.2 W) may be required for the communications link.
- PD 106 may provide a classification signature or classification resistance associated with class 2 (requires power up to 6.49 W), rather than requiring a signature for class 3 (which requires power between 6.49 W to 12.95 W).
- PD 106 measuring or determining an actual length of the communications link, a different classification signature or classification resistance may be provided by PD 106 , which may result in PD 106 being classified differently by PSE 102 , and a lower (or different) amount of power may be allocated or required by PSE 102 .
- PSE 102 may classify PD 106 as a class 2 device based on the adjusted classification signature provided by PD 106 .
- PSE 102 may be required to allocate only 6.49 W to PD 106 , rather than 12.95 W, based on a determination of a propagation delay or length of the communications link. This may save power at PSE 102 , or may allow PSE 102 to power more devices for the same power budget, or may allow PSE 102 to re-allocate this saved power to other devices.
- a PSE and/or a PD may determine a propagation delay of a communications link that connects to the PSE and PD based on a message exchange to determine a packet delay across the communications link.
- the propagation delay for the communications link may be measured or determined as a packet delay from PSE to PD, or the packet delay from PD to PSE, or an average of these two delays, as examples.
- a propagation delay for a communications link may be determined by a PSE or PD based on a message exchange (e.g., synchronization message exchange or other message exchange) between a PSE and PD in accordance with (or compliant or consistent with) IEEE 802.1AS, such as a propagation time measurement using Pdelay (or delay) mechanism, for example.
- a message exchange e.g., synchronization message exchange or other message exchange
- IEEE 802.1AS such as a propagation time measurement using Pdelay (or delay) mechanism, for example.
- FIG. 3 is a timing diagram illustrating a technique that may be used to determine a propagation delay of a communications link based on a message exchange between two nodes according to an example embodiment.
- nodes A and Band shown, and each node (node A, node B) may include a local clock.
- Each node may be a PD or a PSE.
- node A may be a PSE and node B a PD, or node A may be a PD and node B a PSE, for example.
- the technique of FIG. 3 may begin with node A (or the requesting node or device) generating a time stamp, t 1 , for a delay request message 310 .
- the responder, or node B receives this delay request message 310 , and time stamps it with the time of receipt, time t>(or records the time t 2 of receipt of message 310 ).
- the responder, or node B returns a delay response message 320 to node A, and records the transmission time t 3 (or generates a time stamp t 3 at the time of transmission of message 320 ).
- Node B includes the time stamp t 2 in the delay response message 320 .
- Node A receives the delay response message 320 , and time stamps it upon receipt, with a receipt time t 4 .
- Node B also includes the time stamp t 3 in a delay response follow-up message 330 , which is received by node A.
- times t 1 and t 4 may be specific to node A's local clock, while times t 2 and t 3 may be specific to node B's clock.
- times t 1 and t 4 may be specific to node A's local clock
- times t 2 and t 3 may be specific to node B's clock.
- the propagation delay from node A to node B may be referred to as t AB
- the propagation delay from node B to node A may be referred to as t BA
- the mean propagation delay (or propagation time) between nodes A and B across the communications link may be determined based on the following equations.
- the local clocks for nodes A and B may not be synchronized, so the mean propagation delay may be calculated as:
- t 4 ⁇ t 1 may be the total transmission time for messages 310 and 320 (including internal delays at node B), and t 3 ⁇ t 2 may be the internal processing delay at node B (e.g., the time between receipt of message 310 and transmission of message 320 ). Subtracting these two values may provide the total (or sum) propagation delay for both directions, as a sum. This sum may then be divided by 2 to obtain an average or mean propagation delay for the communications link connecting a PSE and PD (or between nodes A and B).
- the accuracy of this calculation of mean (or average) propagation delay for the communications link may be impacted by, for example, how short the interval is for t 3 ⁇ t 2 , how accurately the times t 1 , t 2 , t 3 , and t 4 are measured, how close the frequencies of the clocks of node A and node B are, and any additional internal delays at nodes A and B.
- This merely illustrates one example technique for measuring or determining a propagation delay for a communications link, and many other techniques may be used.
- FIG. 4 is a flow chart illustrating operation of a power source equipment according to an example embodiment.
- the power source equipment PSE may determine a propagation delay of the communications link based on a message exchange between the PSE and the PD, the PSE and PD being connected via the communications link.
- the PSE may determine an amount of power to be supplied via POE from the PSE to the PD via the communications link based on the propagation delay of the communications link.
- an apparatus at a power source equipment may include a transceiver configured to transmit and receive data via a communications link with a powered device (PD), and a controller configured to: determine a propagation delay of the communications link based on a message exchange between the PSE and the PD, the PSE and PD being connected via the communications link; and determine an amount of power to be supplied via Power Over Ethernet (POE) from the PSE to the PD via the communications link based on the propagation delay of the communications link.
- PSE power source equipment
- the controller may include a controller being configured to determine a power classification of the PD, and wherein the controller being configured to determine an amount of power to be supplied via POE from the PSE to the PD may include the controller being configured to determine an amount of power to be supplied via Power Over Ethernet (POE) from the PSE to the PD via the communications link based on the power classification of the PD and the propagation delay of the communications link.
- POE Power Over Ethernet
- the controller may be configured to determine a propagation delay based on a message exchange to determine a packet delay across the communications link.
- the controller may be configured to determine a propagation delay based on a synchronization message exchange in accordance with IEEE 802.1 AS to determine a packet delay across the communications link.
- the PSE may also include a power supply, the controller being further configured to control the power supply to supply the determined amount of power to the PD via POE.
- FIG. 5 is a flow chart illustrating operation of a PSE according to another example embodiment.
- Operation 510 may include determine a classification current in response to a classification load provided on the communications link by the PD, the communications link connecting the PD and the PSE.
- Operation 520 may include performing a power classification of the PD based on the classification current.
- Operation 530 may include determining a propagation delay for the communications link.
- Operation 540 may include determining an amount of power to be supplied via Power Over Ethernet (POE) from the PSE to the PD via the communications link based on the power classification of the PD and the propagation delay of the communications link.
- POE Power Over Ethernet
- an apparatus at a power source equipment may include a transceiver configured to transmit and receive data via a communications link with a powered device (PD), and a controller configured to: determine a classification current a in response to a classification load provided on the communications link by the PD, the communications link connecting the PD and the PSE; perform a power classification of the PD based on the classification current; determine a propagation delay for the communications link; and determine an amount of power to be supplied via Power Over Ethernet (POE) from the PSE to the PD via the communications link based on the power classification of the PD and the propagation delay of the communications link.
- PSE Power Over Ethernet
- the transceiver may include an Ethernet transceiver.
- the controller may be configured to determine a propagation delay for the communications link based on a synchronization message exchange between the PSE and the PD.
- the controller may be configured to determine a propagation delay for the communications link based on a synchronization message exchange between the PSE and the PD in accordance with IEEE 802.1AS.
- the controller may be configured to determine a propagation delay for the communications link based on an average of the propagation delay from the PSE to the PD and the PD to the PSE over the communications link.
- the controller being configured to determine an amount of power to be supplied via Power over Ethernet from the PSE to the PD may include the controller being configured to: determine, based on the link propagation delay for the communications link, a length of the communications link; and determine an amount of power to be supplied via Power over Ethernet from the PSE to the PD via the communications link based on the power classification of the PD and the length of the communications link.
- the controller being configured to determine an amount of power to be supplied via Power over Ethernet from the PSE to the PD may include the controller being configured to: determine, based on the link propagation delay for the communications link, a length of the communications link; determine if the length of the communications link is greater than or equal to a threshold length; determine a first amount of power to be supplied to the PD if the communications link has a length that is greater than or equal to the threshold length; and determine a second amount of power to be supplied to the PD if the length of the communications link is less than the threshold length, the second amount of power being less than the first amount of power.
- the controller being configured to determine an amount of power to be supplied via Power over Ethernet from the PSE to the PD may include the controller being configured to: determine, based on the link propagation delay for the communications link, a length of the communications link; determine if the length of the communications link is greater than or equal to a threshold length; determine, based on the power classification of the PD and the length of the communications link, a first amount of power to be supplied to the PD associated with the power classification of the PD if the communications link has a length that is greater than or equal to the threshold length; and determine, based on the power classification of the PD and the length of the communications link, a second amount of power to be supplied to the PD if the length of the communications link is less than the threshold length, the second amount of power being less than the first amount of power.
- the apparatus at the PSE may further include a power supply, the controller being further configured to control the power supply to supply the determined amount of power to the PD via POE.
- FIG. 6 is a flow chart illustrating operation of a PD according to an example embodiment.
- Operation 610 may include determining, based on the link propagation delay for the communications link, a length of the communications link.
- Operation 620 may include determining a classification load for the PD based on a power need of the PD and the length of the communications link.
- Operation 630 may include providing the determined classification load onto the communications link to indicate a requested power to a PSE.
- the PD may determine the propagation delay for the communications link, and then determine a desired or required power for the PD, based on the length of the link or the propagation delay of the communications link. The PD may then send a message to the PSE requesting the amount of power.
- an apparatus at a powered device may include a transceiver configured to transmit and receive data via a communications link with a power source equipment (PSE), and a controller configured to: determine, based on the link propagation delay for the communications link, a length of the communications link; determine a classification load for the PD based on a power need of the PD and the length of the communications link; and provide the determined classification load onto the communications link to indicate a requested power to a PSE.
- PSE power source equipment
- the controller configured to determine, based on the link propagation delay for the communications link, a length of the communications link may include the controller configured to determine a propagation delay for the communications link based on a synchronization message exchange between the PSE and the PD in accordance with IEEE 802.1AS, and to determine a length of the communications link.
Abstract
Description
- The present application is a continuation of U.S. patent application Ser. No. 12/115,822 entitled “Variable Power Over Ethernet Based on Link Delay Measurement,” filed on May 6, 2008, which claims the benefit of priority under 35 U.S.C. §119 from U.S. Provisional Patent Application Ser. No. 61/028,776 entitled “Variable Power Over Ethernet Based on Link Delay Measurement,” filed on Feb. 14, 2008, the disclosures of which are hereby incorporated by reference in their entirety for all purposes.
- Ethernet communications provide high speed data communications over a communications link between communication nodes (or network devices) that are operating according to the IEEE 802.3 Ethernet standard. The communications medium between the two nodes can be twisted pair wires for Ethernet, or other types of communications medium that are appropriate. Powers over Ethernet (POE) communication systems, based on IEEE 802.3af, may provide power and data communications over a common communications link. More specifically, a power source device (e.g., power source equipment (PSE)) connected to the physical layer of the first node of the communications link provides DC power (for example, 48 volts DC) to a powered device (PD) at the second node of the communications link. The DC power is transmitted simultaneously from PSE to PD over the same communications medium that high speed data is transmitted between PD and PSE. In this manner, a separate power cable may be avoided or unnecessary for the PD.
- The PSE device may be a data switch, a computer, or other device, for example. APSE may include one or more data ports (or Ethernet ports). Each port may include a transceiver to transmit and receive data over a data link or communications medium (e.g., one or more twisted pair wires, or Ethernet cable) that may be connected to a data port on another device or node. Herein, data ports and their corresponding links can be interchangeably referred to as data channels, communication links, data links, etc, for ease of discussion.
- Typical PD devices that use POE to receive power may include a wide variety of devices, such as, for example, Internet Protocol (IP) phones (Voice over IP (VoIP) phones), wireless access points, personal computing devices, such as a personal computer or a laptop computer, handheld devices, a camera (e.g., IP security camera), a print server, or other electronic device. Each type of PD may have a different power requirement. For example, the power requirements of personal computing devices (e.g., laptops) are typically significantly higher than that of VoIP phones, wireless access points, and other limited purpose devices (e.g., print server). In addition, a personal computing device may change its power draw depending on its application load. Moreover, personal computing devices can power other devices such as USB devices or external drives, for example, which will affect total power draw.
- A PSE device (e.g., a PSE switch) may typically have a POE power budget, which may indicate a maximum amount of power (e.g., 200 W) available to provide to one or more connected PDs (connected via one or more Ethernet ports). IEEE 802.3af allows a maximum length of 100 meters for an Ethernet cable or link between aPSE and PD. In allocating power to a PD, PSE devices typically assume that each PD is connected via a maximum length (1OOm) cable. Although, in some cases, PDs may be connected to the PSE via shorter length links or cables. By assuming a 100 meter (or maximum length) link or cable for all connected PDs, this may cause a PSE to allocate to each PD a greater amount of power than is necessary. This may unnecessarily decrease the number of PDs that may be supported or the amount of power that is available for other PDs.
- Various embodiments are disclosed relating to variable power over Ethernet based on a link delay measurement.
-
FIG. 1 is a high level illustration of a Power over Ethernet (POE)system 100 that provides both DC power and data communications over a common data communications medium according to an example embodiment. -
FIG. 2 provides a more detailed circuit diagram of thePOE system 100, wherePSE 102 provides DC power toPD 106 overconductor pairs -
FIG. 3 is a timing diagram illustrating a technique that may be used to determine a propagation delay of a communications link based on a message exchange between two nodes according to an example embodiment. -
FIG. 4 is a flow chart illustrating operation of a power source equipment according to an example embodiment. -
FIG. 5 is a flow chart illustrating operation of a PSE according to another example embodiment. -
FIG. 6 is a flow chart illustrating operation of a PD according to an example embodiment. -
FIG. 1 is a high level illustration of a Power over Ethernet (POE)system 100 that provides both DC power and data communications over a common data communications medium according to an example embodiment. Referring toFIG. 1 , power source equipment (PSE) 102 provides DC power overconductors electrical load 108. The PSE 102 and PD 106 also include data transceivers (transmitter/receiver) that transmit and receive data according to, e.g., IEEE 802.3 Ethernet standard. The term POE herein may refer to providing power over a communications link either for Ethernet or other networking standard. Also, a more general term may be, for example, power over networking, which may include providing power over any networking or communications link (including POE). More specifically, thePSE 102 includes a physical layer device on the PSE side that transmits and receives high speed data with a corresponding physical layer device in thePD 106. Accordingly, the power transfer between thePSE 102 and thePD 106 may occur simultaneously with the exchange of high speed data over theconductors - In an example embodiment, the
conductor pairs conductor pairs conductor pairs -
FIG. 2 provides a more detailed circuit diagram of thePOE system 100, wherePSE 102 provides DC power toPD 106 overconductor pairs PSE 102 includes a transceiver physical layer device (or PHY) 202 having full duplex transmit and receive capability throughdifferential transmit port 204 anddifferential receive port 206. (Herein, transceivers may be referred to as PHYs.) Afirst transformer 208 couples high speed data between thetransmit port 204 and thefirst conductor pair 104. Likewise, asecond transformer 212 couples high speed data between thereceive port 206 and thesecond conductor pair 110. Therespective transformers transceiver 202, but isolate any low frequency or DC voltage from the transceiver ports, which may be sensitive to large voltage values. - The
first transformer 208 includes primary and secondary windings, where the secondary winding (on the conductor side) includes acenter tap 210. Likewise, thesecond transformer 212 includes primary and secondary windings, where the secondary winding (on the conductor side) includes acenter tap 214. TheDC voltage supply 216 generates an output voltage that is applied across the respective center taps of thetransformers center tap 210 is connected to a first output of aDC voltage supply 216, and thecenter tap 214 is connected to a second output of theDC voltage supply 216. As such, thetransformers DC supply 216 from thesensitive data ports transceiver 202. An example DC output voltage is 48 volts, but other voltages could be used depending on the voltage/power requirements of thePD 106. - The
PSE 102 further includes aPSE controller 218 that controls theDC voltage supply 216, e.g., based on a classification load provided by the PD (based on the POE classification of the PD) and/or based on a determined length (or link delay or propagation delay) of a communications link (e.g. Ethernet cable) connecting thePD 106 andPSE 102. As described in greater detail below, the length of the cable or communications link connecting thePSE 102 andPD 106 may be determined based on a propagation time for a packet transmitted across the communications link that connects thePD 106 andPSE 102. For example, ifPSE 102 determines that the communications link (includingconductor pairs 104, 110) betweenPD 106 andPSE 102 is shorter than the maximum length of 1OOm, then the PSE may provide less, or may decrease, power to the PD. - Further, the
PSE controller 218 may detect and validate a compatible PD, determine a power classification signature for the validated PD, determine a length of a communications link or cable between the PSD and PD, determine an amount of power to be supplied to the PD, and provide or supply power to the PD, monitors the power, and reduces or removes the power from the PD when the power is no longer requested or required. During detection, if the PSE finds the PD to be non-compatible, the PSE can prevent the application of power to that PD device, protecting the PD from possible damage. - Still referring to
FIG. 2 , the contents and functionality of thePD 106 will now be discussed. ThePD 106 includes a transceiverphysical layer device 219 having full duplex transmit and receive capability through differential transmitport 236 and differential receiveport 234. Athird transformer 220 couples high speed data between thefirst conductor pair 104 and the receiveport 234. Likewise, afourth transformer 224 couples high speed data between the transmitport 236 and thesecond conductor pair 110. Therespective transformers transceiver 219, but isolate any low frequency or DC voltage from the sensitive transceiver data ports. - The
third transformer 220 includes primary and secondary windings, where the secondary winding (on the conductor side) includes acenter tap 222. Likewise, thefourth transformer 224 includes primary and secondary windings, where the secondary winding (on the conductor side) includes acenter tap 226. The center taps 222 and 226 supply the DC power carried overconductors representative load 108 of thePD 106, where theload 108 represents the dynamic power draw needed to operatePD 106. A DC-DC converter 230 may be optionally inserted before theload 108 to step down the voltage as necessary to meet the voltage requirements of thePD 106. Further, multiple DC-DC converters 230 may be arrayed in parallel to output multiple different voltages (3 volts, 5 volts, 12 volts, for example) to supplydifferent loads 108 of thePD 106. - The
PD 106 further includes aPD controller 228 that monitors the voltage and current on the PD side of the POE configuration. ThePD controller 228 further provides the necessary impedance signatures (e.g., a resistance of approximately 25 kilo-ohms) on thereturn conductor 110 during initialization, so that thePSE controller 218 will recognize the PD as a valid POE device, and be able to classify its power requirements. - During ideal operation, a direct current (IDC) 238 flows from the
DC power supply 216 through thefirst center tap 210, and divides into a first current (I1) 240 and a second current (I2) 242 that is carried overconductor pair 104. The first current (I1) 240 and the second current (I2) 242 then recombine at thethird center tap 222 to reform the direct current (IDC) 238 so as to powerPD 106. On return, the directcurrent NO 238 flows fromPD 106 through thefourth center tap 226, and divides for transport overconductor pair 110. The return DC current recombines at thesecond center tap 214, and returns to theDC power supply 216. As discussed above, data transmission between thePSE 102 and thePD 106 occurs simultaneously with the DC power supply described above. Accordingly, in an example embodiment, afirst communication signal 244 and/or asecond communication signal 246 are simultaneously differentially carried via the conductor pairs 104 and 110 between thePSE 102 and thePD 106. It is important to note that the communication signals 244 and 246 are differential signals that typically are not affected by the DC power transfer. - As stated earlier, detection and power classification of a PD may be a part of the process of supplying power to a PD using POE. The
PD controller 228 further provides the necessary impedance signatures (e.g., a resistance of approximately 25 kilo-ohms) on thereturn conductor 110 during initialization, so that thePSE controller 218 will recognize the PD as a valid POE device. - In an example embodiment, the
PSE 102 may determine an amount of power to be provided toPD 106 via POE based at least in part on a determined link delay or length of the communications link (104, 110) connectingPD 106 andPSE 102. EitherPSE 102 and/orPD 106 may determine a length of a communications link or a propagation delay of the communications link (conductors 104, 110) that connectsPD 106 andPSE 102. For example, the amount power to be provided toPD 106 may be determined (e.g, at least in part) based on both a power classification and a length of the communications link (or link delay). Or, in another example embodiment, a classification load or signature supplied byPD 106 may be varied or adjusted based on the determined length of the communications link or the propagation delay of the communications link that connectsPD 106 andPSE 102, or other power adjustment or selection may be performed based on a determined link delay or length of the communications link, as described in greater detail below. POE Power classification will be described, followed by a description of measuring or determining a communications link delay (or propagation delay) or measuring the length of the communications link (conductors 104, 110), and then adjusting or determining the POE power supplied to thePD 106 based, at least in part, on the length of the communications link or propagation delay of the communications link. - During an optional power classification,
PD controller 228 ofPD 106 may provide a classification signature (or classification load or classification resistance) onto the line, e.g., ontoconductor 110 to indicate power requirements of thePD 106, for example. During power classification, thePSE 102 may apply a voltage, e.g., across the conductors orcommunication links PSE 102 and Rclass is the classification load (resistance) or classification signature applied byPD 106 during the power classification. According to IEEE 802.3af, the power range provided by a PSE depends on the resulting classification current detected by the PSE, e.g., according to Table 1 below. Thus, applying a larger classification resistance may typically result in a lower classification current. Also, in the absence of classification, aPSE 102 may typically need to allocate the maximum power of 12.95 W to thePD 106. Table 1 merely illustrates some example power and current values for different PD classifications, and the disclosure is not limited thereto. -
TABLE 1 Min Max Min Max classification classification Power to Power to current current Class Usage PD (W) PD (W) (mA) (mA) 0 Default .44 12.95 0 4 1 Optional .44 3.84 9 12 2 Optional 3.84 6.49 17 20 3 Optional 6.49 12.95 26 30 4 reserved reserved reserved 36 44 - According to an example embodiment, a
PSE 102 may determine or measure a length of a communications link (e.g., length of an Ethernet cable or length ofconductors 104, 110) connected between thePSE 102 and a connectedPD 106. ThePSE 102 may then adjust (e.g., decrease) an amount of power provided via POE to thePD 106 based on the length of the communications link. - In an example embodiment,
PSE controller 218 ofPSE 102 may determine a length of a communications link (e.g.,conductors 104, 110) based on a propagation delay across the link (or link delay). Once the propagation delay across the link is known, the length of the link may be determined. For example, the length of a communications link (e.g., lengths of the Ethernet cable orconductors PD 106 and PSE 102) may be determined based on Eqn. (1), for example. -
Length(of communications link)=(prop. delay)(⅔ C) Eqn. (1) - Where prop. delay is the measured or determined propagation delay for the link (in seconds), and C is the speed of light (approximately 3×108 meters/second). In this example, the propagation speed on the link has been determined to be ⅔ of the speed of light, or ⅔C.
- In an example embodiment, the
PSE 102 may then determine or adjust (or vary) the power supplied to thePD 106 via POE based on the length of the communications link connectingPSE 102 and PD 106 (or based on the link delay). There are several different ways in whichPSE 102 may adjust or decrease the amount of power supplied to the PD. For example, for a maximum power of 3.84 W (watts) to be supplied toPD 106 as part ofclass 1, a portion of this allocated power may be required by the PD 106 (e.g., 1.84 W), and the remainder (2 W) may be required to provide such power via the 100 meter communications link, since power will be consumed or dissipated (via the link) to provide power to thePD 106 via the link due to the resistance of the communications link. This is merely an example, and other numbers for power may be used. The total resistance of the communications link may typically increase as the length of the link increases. Thus, for a simple example, a 1 OOM link may have approximately twice as much resistance as a 50M link, assuming the links are otherwise the same or very similar. - Thus, in an example embodiment, 3.84 W maximum power may be specified, including 1.84 W to be provided to the
PD 106, plus a total link power of 2 W may be used for the link (in this example), assuming a maximum length 1OOm link. However, if the link is determined to be only 50 M, then thePSE 102 may decrease the supplied (or allocated) power by 1 W (to 2.84 W). Alternatively, if the lengths of the cable is only 10 meters, then only 1/10th of the power allocated to the cable (0.2 W in this example) may be necessary to supply the 1.84 W toPD 106. Thus, in such example, the supplied power may be decreased from 3.84 W to 2.04 W due to use of a shorter communications link or Ethernet cable to connectPD 106 andPSE 102. There are many different ways in which a propagation delay and/or determined length for a communications link may be used to adjust or decrease supplied POE (or power over network) power. This is merely one example technique and others may be used as well to determine a power savings due to a shorter or actual length of the link or Ethernet cable. - By adjusting the POE supplied power based on the actual or determined length of the communications link (e.g., based on the propagation delay for the communications link) that connects the
PD 106 andPSE 102, a lower and more accurate amount of power may (at least in some cases) be allocated byPSE 102 toPD 106 from the PSE's power budget. Thus, measuring or estimating the length of the communications link based on the propagation delay may allow a more accurate determination of the actual power required for the connectedPD 106. This may allow unused power in the PSE's power budget to be used to power additional PDs, or may allow a PSE to power a same number of PDs using a lower amount of power or using a smaller power supply, for example. - In a similar manner,
PD 106 may measure or determine a length of the communications link (e.g., length ofconductors 104, 110) or Ethernet cable that connectsPD 106 andPSE 102 based on the propagation delay for the communications link.PD 106 may determine or estimate a length of the communications link that connectsPD 106 andPSE 102, e.g., based on Eqn. (1), or using other technique. OncePD 106 knows the actual link length,PD 106 may send a packet toPSE 102 indicating the actual length of the communications link or the propagation delay of the communications link (or associated reduction in power if a cable shorter than 100 m is used), or indicating an actual power to be supplied toPD 106.PSE 102 may then adjust the power supplied toPD 106 based on the actual length of the link (or based on link propagation delay) ifPD 106 has indicated the length of the communications link (or propagation delay for the link), orPSE 102 may supply the requested power toPD 106 ifPD 106 has indicated a requested power (taking into account length of the communications link). - Alternatively,
PD 106 may provide a classification resistance or classification signature toPSE 102 based, at least in part, on the actual or measured length of the communications link or based on the measured or determined propagation delay for the communications link that connectsPD 106 andPSE 102. For example,PD 106 may require a base power of 6 W (for the PD itself), plus 2 W associated with a maximum link length of 100 meters, requiring a total power of 8 W to be supplied by thePSE 102. If a communications link of length equal to 10 meters is used to connectPD 106 and PSE 102 (instead of 100 meters), a power savings of 1.8 W may result (for example), since only 10% of 2 W (or 0.2 W) may be required for the communications link. This may decrease the total power requirement forPSE 102 forPD 106 from 8 W to 6.2 W, in this simple example. Thus, in this example, due to the decrease in total power requirements from 8 W to 6.2 W,PD 106 may provide a classification signature or classification resistance associated with class 2 (requires power up to 6.49 W), rather than requiring a signature for class 3 (which requires power between 6.49 W to 12.95 W). Thus, byPD 106 measuring or determining an actual length of the communications link, a different classification signature or classification resistance may be provided byPD 106, which may result inPD 106 being classified differently byPSE 102, and a lower (or different) amount of power may be allocated or required byPSE 102. For example,PSE 102 may classifyPD 106 as a class 2 device based on the adjusted classification signature provided byPD 106. Thus, in this example,PSE 102 may be required to allocate only 6.49 W toPD 106, rather than 12.95 W, based on a determination of a propagation delay or length of the communications link. This may save power atPSE 102, or may allowPSE 102 to power more devices for the same power budget, or may allowPSE 102 to re-allocate this saved power to other devices. - According to an example embodiment, a PSE and/or a PD may determine a propagation delay of a communications link that connects to the PSE and PD based on a message exchange to determine a packet delay across the communications link. The propagation delay for the communications link may be measured or determined as a packet delay from PSE to PD, or the packet delay from PD to PSE, or an average of these two delays, as examples. In an example embodiment, a propagation delay for a communications link may be determined by a PSE or PD based on a message exchange (e.g., synchronization message exchange or other message exchange) between a PSE and PD in accordance with (or compliant or consistent with) IEEE 802.1AS, such as a propagation time measurement using Pdelay (or delay) mechanism, for example.
-
FIG. 3 is a timing diagram illustrating a technique that may be used to determine a propagation delay of a communications link based on a message exchange between two nodes according to an example embodiment. Referring toFIG. 3 , nodes A and Band shown, and each node (node A, node B) may include a local clock. Each node may be a PD or a PSE. For example, node A may be a PSE and node B a PD, or node A may be a PD and node B a PSE, for example. The technique ofFIG. 3 may begin with node A (or the requesting node or device) generating a time stamp, t1, for adelay request message 310. The responder, or node B, receives thisdelay request message 310, and time stamps it with the time of receipt, time t>(or records the time t2 of receipt of message 310). The responder, or node B, returns adelay response message 320 to node A, and records the transmission time t3 (or generates a time stamp t3 at the time of transmission of message 320). Node B includes the time stamp t2 in thedelay response message 320. Node A receives thedelay response message 320, and time stamps it upon receipt, with a receipt time t4. Node B also includes the time stamp t3 in a delay response follow-upmessage 330, which is received by node A. Note, for example, that times t1 and t4 may be specific to node A's local clock, while times t2 and t3 may be specific to node B's clock. Thus, after transmission of all three messages, 310, 320 and 330, that node A will know all four time stamps, t1, t2, t3, and t4. The propagation delay from node A to node B may be referred to as tAB, while the propagation delay from node B to node A may be referred to as tBA. The mean propagation delay (or propagation time) between nodes A and B across the communications link may be determined based on the following equations. -
t AB =t 2 −t 1 (Eqn. 2) -
t BA =t 4 −t 3 (Eqn. 3) - However, the local clocks for nodes A and B may not be synchronized, so the mean propagation delay may be calculated as:
-
T mean-prop=(t AB +t BA)2=[(t 4 −t 1)−(t 3 −t 2)]/2. (Eqn. 4), - Where, t4−t1 may be the total transmission time for
messages 310 and 320 (including internal delays at node B), and t3−t2 may be the internal processing delay at node B (e.g., the time between receipt ofmessage 310 and transmission of message 320). Subtracting these two values may provide the total (or sum) propagation delay for both directions, as a sum. This sum may then be divided by 2 to obtain an average or mean propagation delay for the communications link connecting a PSE and PD (or between nodes A and B). The accuracy of this calculation of mean (or average) propagation delay for the communications link may be impacted by, for example, how short the interval is for t3−t2, how accurately the times t1, t2, t3, and t4 are measured, how close the frequencies of the clocks of node A and node B are, and any additional internal delays at nodes A and B. This merely illustrates one example technique for measuring or determining a propagation delay for a communications link, and many other techniques may be used. -
FIG. 4 is a flow chart illustrating operation of a power source equipment according to an example embodiment. At 310, the power source equipment (PSE) may determine a propagation delay of the communications link based on a message exchange between the PSE and the PD, the PSE and PD being connected via the communications link. At 320, the PSE may determine an amount of power to be supplied via POE from the PSE to the PD via the communications link based on the propagation delay of the communications link. - In another example embodiment, an apparatus at a power source equipment (PSE) may include a transceiver configured to transmit and receive data via a communications link with a powered device (PD), and a controller configured to: determine a propagation delay of the communications link based on a message exchange between the PSE and the PD, the PSE and PD being connected via the communications link; and determine an amount of power to be supplied via Power Over Ethernet (POE) from the PSE to the PD via the communications link based on the propagation delay of the communications link.
- In an example embodiment, the controller may include a controller being configured to determine a power classification of the PD, and wherein the controller being configured to determine an amount of power to be supplied via POE from the PSE to the PD may include the controller being configured to determine an amount of power to be supplied via Power Over Ethernet (POE) from the PSE to the PD via the communications link based on the power classification of the PD and the propagation delay of the communications link.
- In another example embodiment, the controller may be configured to determine a propagation delay based on a message exchange to determine a packet delay across the communications link.
- In another example embodiment, the controller may be configured to determine a propagation delay based on a synchronization message exchange in accordance with IEEE 802.1 AS to determine a packet delay across the communications link.
- In another example embodiment, the PSE may also include a power supply, the controller being further configured to control the power supply to supply the determined amount of power to the PD via POE.
-
FIG. 5 is a flow chart illustrating operation of a PSE according to another example embodiment.Operation 510 may include determine a classification current in response to a classification load provided on the communications link by the PD, the communications link connecting the PD and the PSE.Operation 520 may include performing a power classification of the PD based on the classification current.Operation 530 may include determining a propagation delay for the communications link.Operation 540 may include determining an amount of power to be supplied via Power Over Ethernet (POE) from the PSE to the PD via the communications link based on the power classification of the PD and the propagation delay of the communications link. - In another example embodiment, an apparatus at a power source equipment (PSE) may include a transceiver configured to transmit and receive data via a communications link with a powered device (PD), and a controller configured to: determine a classification current a in response to a classification load provided on the communications link by the PD, the communications link connecting the PD and the PSE; perform a power classification of the PD based on the classification current; determine a propagation delay for the communications link; and determine an amount of power to be supplied via Power Over Ethernet (POE) from the PSE to the PD via the communications link based on the power classification of the PD and the propagation delay of the communications link.
- In an example embodiment, the transceiver may include an Ethernet transceiver. In another example embodiment, the controller may be configured to determine a propagation delay for the communications link based on a synchronization message exchange between the PSE and the PD.
- In another example embodiment, the controller may be configured to determine a propagation delay for the communications link based on a synchronization message exchange between the PSE and the PD in accordance with IEEE 802.1AS.
- In another example embodiment, the controller may be configured to determine a propagation delay for the communications link based on an average of the propagation delay from the PSE to the PD and the PD to the PSE over the communications link.
- In another example embodiment, the controller being configured to determine an amount of power to be supplied via Power over Ethernet from the PSE to the PD may include the controller being configured to: determine, based on the link propagation delay for the communications link, a length of the communications link; and determine an amount of power to be supplied via Power over Ethernet from the PSE to the PD via the communications link based on the power classification of the PD and the length of the communications link.
- In an example embodiment, the controller being configured to determine an amount of power to be supplied via Power over Ethernet from the PSE to the PD may include the controller being configured to: determine, based on the link propagation delay for the communications link, a length of the communications link; determine if the length of the communications link is greater than or equal to a threshold length; determine a first amount of power to be supplied to the PD if the communications link has a length that is greater than or equal to the threshold length; and determine a second amount of power to be supplied to the PD if the length of the communications link is less than the threshold length, the second amount of power being less than the first amount of power.
- In an example embodiment, the controller being configured to determine an amount of power to be supplied via Power over Ethernet from the PSE to the PD may include the controller being configured to: determine, based on the link propagation delay for the communications link, a length of the communications link; determine if the length of the communications link is greater than or equal to a threshold length; determine, based on the power classification of the PD and the length of the communications link, a first amount of power to be supplied to the PD associated with the power classification of the PD if the communications link has a length that is greater than or equal to the threshold length; and determine, based on the power classification of the PD and the length of the communications link, a second amount of power to be supplied to the PD if the length of the communications link is less than the threshold length, the second amount of power being less than the first amount of power.
- In an example embodiment, the apparatus at the PSE may further include a power supply, the controller being further configured to control the power supply to supply the determined amount of power to the PD via POE.
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FIG. 6 is a flow chart illustrating operation of a PD according to an example embodiment.Operation 610 may include determining, based on the link propagation delay for the communications link, a length of the communications link.Operation 620 may include determining a classification load for the PD based on a power need of the PD and the length of the communications link.Operation 630 may include providing the determined classification load onto the communications link to indicate a requested power to a PSE. - In an alternative embodiment, the PD may determine the propagation delay for the communications link, and then determine a desired or required power for the PD, based on the length of the link or the propagation delay of the communications link. The PD may then send a message to the PSE requesting the amount of power.
- In an example embodiment, an apparatus at a powered device (PD) may include a transceiver configured to transmit and receive data via a communications link with a power source equipment (PSE), and a controller configured to: determine, based on the link propagation delay for the communications link, a length of the communications link; determine a classification load for the PD based on a power need of the PD and the length of the communications link; and provide the determined classification load onto the communications link to indicate a requested power to a PSE.
- In an example embodiment, the controller configured to determine, based on the link propagation delay for the communications link, a length of the communications link may include the controller configured to determine a propagation delay for the communications link based on a synchronization message exchange between the PSE and the PD in accordance with IEEE 802.1AS, and to determine a length of the communications link.
- While certain features of the described implementations have been illustrated as described herein, many modifications, substitutions, changes and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the various embodiments.
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US10969813B2 (en) | 2019-04-15 | 2021-04-06 | Arista Networks, Inc. | Maximum power detection for powered devices |
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US8539255B2 (en) | 2013-09-17 |
US8621250B1 (en) | 2013-12-31 |
US20090210725A1 (en) | 2009-08-20 |
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